The invention is directed generally to improved compositions and methods for preventing corrosion of metal surfaces coming into contact with water. More particularly, the invention is directed to improved compositions and methods for controlling corrosion in aqueous systems with multiple metallurgies in generally continuous contact with water. Industrial cooling systems including recirculating cooling towers and once-through heat exchange coolers represent typical such systems. In an important embodiment, the present invention is directed to a composition exhibiting outstanding corrosion control for mild steel maintained in generally continuous contact with water.
In most aqueous systems in which water is contained and through which water is moved, it is imperative that corrosion of metal surfaces contacting the water be controlled. Unchecked corrosion leads to premature failure of the system through erosion of system components and resultant corrosion penetration and stress failure.
Numerous chemical additives have been developed over the years for controlling corrosion of metals in aqueous systems. Typical such compounds include chromates, orthophosphate, nitrites, silicates, calcium carbonate, polyphosphonates, zinc and organic film-forming amines.
The use of these chemical corrosion inhibitors, however, presents a number of difficulties. Some of these inhibitors are toxic even at very low levels of concentration and are therefore barred from use in certain environments. Some of these compounds are uneconomical to use in high water volume applications such as industrial cooling systems. Perhaps most importantly, most of these inhibitors are specific for certain metallurgies and tend to operate at cross purposes when combined in a single composition or aqueous environment. Since multiple metallurgy equipment such as common industrial cooling systems requires the application of several different corrosion inhibitors, numerous difficulties arise due to physical and chemical interference between the different inhibitors.
Scaling is another problem of concern in systems in which metal surfaces are in generally continuous contact with water. Control of scale formation is of particular importance in recirculating cooling towers and in once-through heat exchange coolers utilizing high hardness water. In such systems scale tends to restrict water movement and heat exchange efficiency while accelerating the rate of metal corrosion. It is therefore important to control scaling, a task usually performed by a class of chemical compounds generally known as scale inhibitors. As might be anticipated, the introduction of scale inhibitors into aqueous systems already carrying multiple corrosion inhibitors will generally impair the effectiveness of all treatments present due to the multiplication of physical and chemical interaction between the different chemical compounds in the system.
Those skilled in the art therefore well recognize the need to develop compositions and methods capable of controlling corrosion in aqueous systems with multiple metallurgies in a safe, economic and efficient manner. If a further corrosion controlling composition and method utilizing scale inhibiting compounds which do not objectionably interfere with the action of the corrosion inhibitors could be developed, another important contribution to the art would be at hand.
It is an important object of the present invention to provide new compositions and methods employing these compositions which offer outstanding corrosion control in aqueous systems with multiple metallurgies.
It is a further object of the present invention to provide new compositions and methods which provide scale inhibition without significantly impairing corrosion control efficiency.
Yet another object of the present invention is to provide new highly efficient mild steel corrosion inhibiting compositions.
Other objects and features of the invention will become apparent upon examination of the following specification together with the claims. While the invention is described below in connection with preferred or illustrative embodiments, these embodiments are not intended to be exhaustive or limiting of the invention. Rather, the invention is intended to cover any alternatives, modifications and equivalents that may be included within its spirit and scope as defined by the appended claims.